Coupled slow waves,slow acoustic waves,and electromagnetic waves are simultaneously achieved based on a piezoelectric material,in which a line defect is created within a honeycomb lattice array of cylindrical holes etched in a LiNbO3 slab.Finite element simulations in frequency domain and time domain demonstrate that a highly localized slow mode is obtained in the defect.Owing to the piezoelectricity of LiNbO3,acoustic and electromagnetic waves are coupled with each other and transmit along the line defect.Therefore,in addition to a slow acoustic wave,an electromagnetic wave with a group velocity even lower than conventional acoustic waves is achieved.